Cabous Eloff scored a last-minute try as the Rebels beat the Force 34-30 in their final regular season game of Super Rugby AU in Newcastle on Saturday to reach the playoffs for the first time.
Eloff was awarded the try after review to give the Rebels the four-point victory they needed to move past the Waratahs into third place of the domestic competition.
The Brumbies, who have already locked up top spot and guaranteed a place in the final on September 19, face the second-placed Reds in Brisbane later on Saturday.
The Reds will play the Rebels next weekend for a spot in the final.
"A little bit of relief and just really proud of the boys, we stuck at it there," said Rebels captain Dane Haylett-Petty. "Credit to the Force, for a long period of the game there they were on top of us and yeah, it was a great effort to fight back and score that try."
The Rebels, who joined Super Rugby in 2011, have never qualified for the playoffs in the broader competition, which included teams from South Africa, New Zealand, Argentina and Japan.
They had their best chances in 2018 and again last year, only to lose their final regular season games.
The Melbourne-based side, needing to win by at least four points, raced to a 20-8 lead just before halftime with tries to winger Tom Pincus and centre Reece Hodge.
The Force, who got an early try to inside centre Henry Taefu, grabbed the momentum with two tries to hooker Andrew Ready either side of halftime to level the score at 20-20.
Ian Prior's second penalty and Brynard Stander's try gave the Force a 10-point advantage and left the Rebels needing to chase the game.
They managed to reduce the deficit when Haylett-Petty crossed but were then held out by some superb defence by the Force until Eloff finally managed to break through.